/Engine/Source/Runtime/Engine/Classes/Engine/StreamableRenderAsset.h
Register a callback to get notified when a certain mip or LOD is resident or evicted.
void RegisterMipLevelChangeCallback ( [UPrimitiveComponent](API\Runtime\Engine\Components\UPrimitiveComponent) * Component, int32 LODIdx, float TimeoutSecs, bool bOnStreamIn, FLODStreamingCallback && Callback )